login
This site is supported by donations to The OEIS Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A062209 Numbers n such that (4*10^n-7)/33 = 121...21 is a smoothly undulating palindromic prime (or PRP). 28
7, 11, 43, 139, 627, 1399, 1597, 1979, 7809, 14059, 46499 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Prime versus probable prime status and proofs are given in the author's table.

No further terms < 100000. - Ray Chandler, Aug 17 2011

The actual primes, called smoothly undulating palindromic primes (cf. links, A032758 and A059758), are listed in A092696. The number of '12's is given in A056803(n) = (a(n)-1)/2. - M. F. Hasler, Jul 30 2015

REFERENCES

J.-M. De Koninck, Ces nombres qui nous fascinent, Entry 139, p. 48, Ellipses, Paris 2008.

LINKS

Table of n, a(n) for n=1..11.

P. De Geest, SUPP Reference Table - 121

Index entries for sequences related to smoothly undulating palindromic primes

EXAMPLE

a(n) = 11 --> (12*10^11-21)/99 = 12121212121.

MATHEMATICA

d[n_]:=IntegerDigits[n]; Length/@d[Select[NestList[FromDigits[Join[d[#], {2, 1}]]&, 1, 1000], PrimeQ]] (* Jayanta Basu, May 25 2013 *)

PROG

(PARI) for(n=1, 1e5, ispseudoprime(5^n<<(n+2)\33)&&print1(n", ")) \\ M. F. Hasler, Jul 30 2015

CROSSREFS

Cf. A062210-A062232, A059758, A032758, A092696, A056803.

Sequence in context: A268579 A129865 A153377 * A086828 A117392 A105867

Adjacent sequences:  A062206 A062207 A062208 * A062210 A062211 A062212

KEYWORD

nonn,base

AUTHOR

Patrick De Geest and Hans Rosenthal (Hans.Rosenthal(AT)t-online.de), Jun 15 2001.

EXTENSIONS

a(11) = 46499 from Ray Chandler, Nov 11 2010

Edited by Ray Chandler, Aug 17 2011

Name and other items edited by M. F. Hasler, Jul 30 2015

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent | More pages
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy .

Last modified September 23 21:16 EDT 2017. Contains 292391 sequences.